The present invention relates to a high spatial resolution scintigraphic device having collimator with integrated crystals, external diagnostic use or for guided surgery applications, requiring the identification of the localization of tumour lesions.
In particular, functional imaging systems with small field of view (see U.S. patent application Ser. Nos. 09/202,894 and 09/202,790 in the name of Alessandro Soluri et al.) can be applied in Nuclear Medicine as location and diagnostic devices, of reduced weight and minimum size, in order to identify neoplasias with high spatial resolution. Use of said devices can also find application in the scintigraphic analysis of small animals, in order to experiment new radio-marked antibodies, specific for particular pathologies. Another field of application relates to the guided localization of prostate and breast lesions, in order to identify the areas with higher uptake to be subjected to bioptic sampling, to integrate current radiographic and/or echographic techniques. Such devices can find further applications in Astrophysics and in industrial non destructive test systems.
In particular, the main use of the device relates to locating tumour lesions, especially in those techniques that require an adequate spatial precision such as biopsies (prostate and breast) or in radio-guided or radio-immune-guided surgery. To remove a tumour lesion, the surgeon needs to identify its location and, for this purpose, he/she normally uses the results of diagnostic investigations performed previously with techniques known as RX, CAT scans, NMR and traditional Scintigraphy. However at the moment of the operation, after xe2x80x9copeningxe2x80x9d the part, the surgeon may need to locate even more precisely the area to be cut or removed and, for this purpose, he/she can employ a so-called xe2x80x9csurgical probexe2x80x9d. After injecting into the patient a radio-pharmaceutical, which has the peculiarity of being fixed more specifically in tumour cells, the surgeon uses a probe to detect the gamma rays emitted by the radioisotope, present in the molecules of the drug in the area examined at a given time. The probe is sensitive to the intensity and energy of the detected gamma radiation and provides analogue signals that are proportional to the radioisotope concentration measured in the region identified by a single channel collimator.
The detected signals are converted to digital form providing information, in a light or sound scale, about the intensity of the signals that fall within the selected energy window. The limitation is constituted by the impossibility of providing an image that describes the spatial map of the concentration of radio-pharmaceutical and that only provides the visualisation of the counts in the area identified by the collimator.
This limitation of current technologies is mainly due to the poor spatial resolution (about 1 cm) and to the considerable dimensions of current commercial gamma-cameras.
Already the devices claimed by Soluri et al. (see U.S. patent application Ser. Nos. 09/202,894 and 09/202,790), in addition to those claimed by Francesco De Notaristefani et al. (WO 96/379791), Sealock et al. (U.S. Pat. No. 5,783,829), Stan Majewski et al. (U.S. Pat. No. 5,864,141), Scibilia et al. (U.S. Pat. No. 6,021,341), propose improvements both in terms of spatial resolution and in terms of reduced size and weight. Nevertheless, in some applications, the required spatial resolution becomes a fundamental parameter, so it is necessary to improve spatial resolution.
One of the current limitations surely consists of the inability to locate in a precise manner the spatial position of events that reach individual elements of the scintillating crystal. Current devices prevalently use photomultipliers, or photo-tubes, of the latest generation, known as PSPMTs (Position Sensitive Photomultiplier Tubes) coupled to crystal matrices located at the output of a lead collimator, general purpose or high resolution, normally with hexagonal holes. Alternatively the scintillating crystals are constituted by planar elements, located at the output of the same types of collimators. In this case, using a planar scintillation crystal with traditional photomultipliers (PMT=Photomultiplier Tube), expected spatial resolutions are definitely inadequate in reference to the diagnostic techniques described above.
Scintillation crystals, with polygonal form and suitable thickness, can be inorganic or organic, both in the hyper-pure state and doped with suitable quantities of appropriate materials in order to boost their scintillation properties (for instance: CsI(Tl), CsI(Na), NaI(Tl)), according to the type of application to be achieved, to the diagnostic techniques and to the tracers employed. In any case, the emission spectrum of the scintillation light must exhibit a good superposition with that of absorption of the photosensitive layer of the photomultiplier.
The main limitation of the prior art consists of the fact that, when employing square section crystal matrices coupled with collimator with hexagonal holes, it is not possible to achieve such a geometric alignment as to guide photons into the specific area of the individual element of the scintillation matrix. A hexagonal hole will allow the passage of photons on a crossing area between multiple individual elements of the scintillation crystal, so that when the position is computed multiple points can be visualised on the image, if spatial resolution is sufficient to separate them. In this way the number of photons integrated for that hole and that have stricken the individual scintillating element is recorded.
One aim of the invention is to obtain a miniaturised imaging system that is optimised and dedicated to individual scintigraphic applications.
Another aim of the invention is to obtain a scintigraphic device, of reduced size, usable also for external diagnoses of tumours of small dimensions (for instance skin melanomas, thyroid pathologies, etc.), and of extremely reduced weight of better ease of handling, with the capability to visualise areas of interest that would be difficult to reach with current devices.
An additional aim of the invention is to obtain a device which, employing crystals associated to collimators, achieves a perfect geometric alignment, such as to guide the photons.
Yet another aim of the invention is to achieve a miniaturised device with high spatial resolution, suitable for use both during surgical operations and as an external diagnostic device for detecting tissues areas invaded by tumour formations of small size.
Therefore, the invention, as it is characterised in the claims that follow, solves the problem of providing a miniaturised high spatial resolution scintigraphic device having collimator with integrated crystals, comprising in succession from an open end of a container coated with a shielding cladding starting from the source of the event to be detected:
a collimator made of a material with high effective atomic number, having internally a multiplicity of equal conduits of determined length, identified and separated by septa of a thickness suitable to the energy of the photons to be detected, terminating in a common end plane on the opposite plane to the source of the event to be measured;
a scintillation crystal structure able to convert the radiation from the source being examined into light radiation;
at least a photomultiplier of the type with crossed anodes or crossed wires receiving the light radiation emitted by the scintillation crystal structure and generating electrical signals proportional to their intensity and identifying the position co-ordinates (X,Y) of the event;
electronic circuits to amplify and integrate the signals generated by the photomultiplier to determine event position co-ordinate and the related energy for the subsequent transfer to the conversion device and hence to an electronic processor that process and displays them on a monitor in the form of an image which, from a general point of view, is characterised in that said scintillation crystal structure is constituted by a multiplicity of individual crystals with polygonal structure, with base faces and lateral surface, each integrally integrated in proximity to the extremity, oriented towards the photomultiplier, of each conduit of the collimator, having conforming polygonal section and positioned in such a way that the base faces of the crystals oriented towards the photomultiplier lie in a same plane, parallel to said common end plane of the collimator.